The invention relates to data communication networks and, more particularly, to bandwidth allocation in digital satellite data communication networks.
In recent years the need for global data networking capability has rapidly expanded. Broadband satellite data communication networks have been proposed as an alternative to existing land-based data communication networks. One type of satellite data communication network is described in a variety of U.S. patents assigned to the assignee of the present invention, including U.S. Pat. Nos. 5,386,953; 5,408,237; 5,527,001; 5,548,294; 5,621,415; 5,641,135; 5,642,122; 5,650,788; 5,736,959 and 5,740,164. These patents and other commonly assigned pending patent applications describe a satellite data communication network that includes a constellation of low-Earth-orbit (LEO) satellites capable of transmitting data from one location on the Earth""s surface to another location. More specifically, each LEO satellite has a communication footprint that covers a portion of the Earth""s surface as a satellite passes over the Earth. The communication footprint defines the area of the Earth within which ground terminals can communicate with the satellite. During the period of time a ground terminal remains within the border of a satellite""s footprint, the ground terminal may transmit data to and receive data from the xe2x80x9cservicingxe2x80x9d satellite. When a satellite reaches the end of its servicing arc and the ground terminal passes outside the satellite""s communication footprint, another satellite in orbit is positioned to service the ground terminal previously covered by the satellite reaching the end of its servicing arc.
Data to be sent from one location to another location on the Earth is transmitted from a ground terminal to the LEO satellite servicing the ground terminal via an uplink data channel. The data is routed through the constellation of LEO satellites to the satellite servicing the ground terminal that is to receive the data. The latter satellite transmits the data to the receiving ground terminal via a downlink data channel. Thus, the constellation of LEO satellites and the ground terminals form a satellite data communication network wherein the ground terminals and satellites form nodes of the network.
Existing data communication networks that use geosynchronous satellites for data transmission are subject to numerous disadvantages in comparison to a LEO satellite network. By their nature, geosynchronous satellites are located at a very high altitude (37,000 km) from the Earth. Because of the distance involved, both uplink and the downlink transmission times to the geosynchronous satellite are significant. For many applications requiring timely delivery of data signals, the amount of delay introduced by geosynchronous satellite communication is often dissatisfying or unacceptable. Geosynchronous satellite communication also requires a high power ground terminal to be able to communicate with the geosynchronous satellite.
Since LEO satellites orbit the Earth at a much lower altitude than a geosynchronous satellite, data signals communicated via LEO satellites do not travel the same amount of distance and therefore do not experience as much time in transmission. LEO satellites also cost much less to put into orbit and are able to communicate with lower power ground terminals. Nevertheless, communication via LEO satellites has its own set of challenges to address, primarily due to the fact that the orbit of a LEO satellite does not match the rotation of the Earth. The constant orbital motion of LEO satellites passing in and out of range of a particular ground terminal on the Earth not only affects the allocation of transmission resources and scheduling of data transmissions in the LEO satellite network but also affects the routing of data transmissions between satellites and the receiving ground terminal.
Problems with scheduling and routing of data transmissions, as well as inefficient allocation of transmission capacity, are present in other existing data communication networks. For instance, while the global interconnection of computer networks known as the Internet routes data packets with the anticipation that the packets will eventually be received by the intended receiver, it is not uncommon for packets to be lost or delayed during transmission. There is no guarantee if or when a packet will be actually delivered to an intended receiver. Only a xe2x80x9cbest effortxe2x80x9d is given to the transmission of data, regardless of the relative importance given by the sender to the transmission.
Moreover, the current Internet does not differentiate between different types of data being transmitted. For example, data packets requiring delivery within a certain time frame (e.g., for real-time video or audio communication) receive no preference in transmission over packets that generally do not require a particular time of delivery (e.g., electronic mail). Similarly, data packets carrying important information for which packet loss cannot be tolerated (e.g., medical images) receive no greater priority than other data packets. Because all data packets are viewed as equally important in terms of allocating transmission resources, less critical transmissions, such as e-mail, may serve to delay or displace more important and time-sensitive data.
Furthermore, capacity for data transmission in existing data communication networks is often inefficiently allocated. In some instances, transmission capacity, or bandwidth, is allocated to a particular user according to a fixed schedule or particular network setup, but the bandwidth is not actually used. In other instances, a user is precluded from transmitting a burst of data that, for the moment, exceeds the user""s bandwidth allocation. Existing data communication networks have lacked mechanisms whereby bandwidth may be allocated on-demand.
The present invention is a system and method for allocating transmission capacity, or bandwidth, in a LEO satellite data communication network. More specifically, the present invention provides a priority-based system and method of allocating bandwidth for uplink transmission of one or more data packets from a ground terminal to a servicing satellite in the LEO satellite data communication network. Uplink bandwidth is allocated based on a priority status assigned to the data packets to be transmitted. It is intended that the uplink bandwidth, once allocated for transmission of data packets, will enable the data transmission to meet or exceed a user-selected standard of data transmission service (otherwise referred to as a xe2x80x9cquality of servicexe2x80x9d). Different data packets in a data transmission may be assigned different levels of priority status so that the overall data transmission meets or exceeds the selected quality of service.
Prior to transmitting a data packet via an uplink signal to a servicing satellite overhead, the ground terminal first obtains an allocation of uplink signal bandwidth to transmit the data packet. Uplink bandwidth is preferably divided into slots representing time and signal frequency and is allocated for transmission of data packets in accordance with the assigned priority status of the data packets. Bandwidth for transmitting higher priority data packets is allocated before bandwidth for transmitting data packets with a lower priority status.
The system and method of the present invention provide a bandwidth-on-demand feature. Bandwidth for uplink transmission is allocated on request. Likewise, previously allocated uplink bandwidth may be deallocated on request. In one embodiment of the invention, a bandwidth allocation processor onboard a LEO satellite receives and processes bandwidth allocation requests sent to the satellite. The bandwidth allocation processor reports bandwidth allocations to the requesting ground terminals so that the ground terminals may transmit data packets having a corresponding priority status at the allocated time and frequency.